- Kuzan left the marines. The entire point of his character (as he himself pointed out) is to do things without being in the Marines. By being leader of the SWORD, he's automatically under Sakazuki as Sakazuki is the leader of the Marines, and SWORD is an official sanctioned unit of the Marines. No different than the "Special Science Unit".
- Why would Sakazuki mention Drake when there's been no need to mention Drake? The entire point is they're a special task force, its' more than likely outside of the Fleet Admiral they don't know about it. The other time was during the conversation in front of tons of Marine officers, he's not gonna blow up Drake's cover then and there.
Honestly people are looking WAY too much into it, especially with the "anti-WG" stuff, when there's been nothing talked about that or implied about that. US military for example has secret task units as well, which are all under the respective branch leaders & then under the Commander-In-Chief of all US Military.
The only other person outside of Sakazuki who the SWORD would be under is Sengoku, but Sengoku himself said to Kong it's time for the new generation of Marines to run their Justice, so it wouldn't make sense for Sengoku to keep it hidden from Sakazuki, and then even tease Sakauzki about how hard it is to be a fleet admiral. There is also the blatant tatoo of a sword on Sakazuki's bicep that stands out like all hell. The "SWORD" isn't anything that was created post-TS, it's a unit that's been there for a hot minute, as Drake during the entire pre-TS was simply an undercover Marine, meaning the unit existed back then as well.
But none of that would make Sengoku or Sakazuki the "leaders" of the SWORD, as the leader of the unit is the captain of the unit, which in this case is Drake.